There has hitherto been known a power transfer device that includes a reservoir plate that partitions a space in a case member that houses a speed change mechanism and a differential device (differential gear) into a differential chamber, in which the differential device is disposed, and a storage chamber, in which oil (working oil) is stored (see Patent Document 1, for example). In the power transfer device, the reservoir plate is disposed so as to cover the differential device in the case member and tightly contact the inner peripheral surface of a rib member that extends from the case member along the outer peripheral surface of a ring gear (differential ring gear) of the differential device. Consequently, in the power transfer device, a residence of oil in the differential chamber, that is, around the ring gear of the differential device, is suppressed to suppress an increase in rotational resistance of the ring gear.